This research will develop methods to model active sites in metalloproteins for the purpose of determining fundamental structure-function relationships for how proteins activate dioxygen, a process that strongly impacts human health and aging. Artificial metallproteins will be prepared utilizing biotin-streptavidin technology as a tool to ensure specific and reproducible placement of synthetic metal complexes within protein hosts. This approach is proposed to be an effective method to model key properties of the active sites in native metalloproteins, including site isolation of species, regulation of the primary coordination sphere, and control of the microenvironments around the metal complexes. One glaring weakness of many biomimetic systems is their limited ability to regulate the microenvironments that surround metal centers. No chemical system operates in isolation without interacting with its local environment. There is a growing body of evidence from structural biology that the microenvironment, a space around metal complexes that comprises the secondary coordination sphere, has profound effects on protein function that ranges from modulation of physical properties to delivery of reactants and removal of products. It is our contention that the greater regulation of microenvironments will lead to better understanding of protein function. It is further maintained that the benefits gained from fundamental analyses as proposed in this application extend well beyond improvements in selectivities/efficiencies at the molecular level ? they are transformative for all types of platforms, providing the requisite information that is still missing for the development of highly functional systems. We propose an approach for preparing artificial metalloproteins that allows for the confinement of synthetic complexes within protein hosts to regulate both the primary and secondary coordination spheres about the immobilized metal centers. The ability to regulate these coordination spheres within a protein will produce systematic structure-function relationships that will lead to an improved understanding of chemical processes that are directly linked to human health.